#define _CRT_SECURE_NO_WARNINGS 1
/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2)
    {
        ListNode* cur1 = l1, * cur2 = l2;
        ListNode* ret_node = new ListNode;
        ListNode* ret_node_tail = ret_node;

        int tmp = 0;
        while (cur1 || cur2 || tmp)
        {
            if (cur1)
            {
                tmp += cur1->val;
                cur1 = cur1->next;
            }
            if (cur2)
            {
                tmp += cur2->val;
                cur2 = cur2->next;
            }
            ListNode* new_node = new ListNode(tmp % 10);
            ret_node_tail->next = new_node;
            tmp = tmp >= 10 ? 1 : 0;
            ret_node_tail = ret_node_tail->next;
        }
        return ret_node->next;
    }
};